Meringue is due to finish his treatment today - 1 tsp aq salt per gallon for fin regrowth/infection protection. Do I need to do anything special to transition him from the treated water to regular conditioned water? I.e., do I just plop him back in after a water change or should I do a slow acclimatization?

Usually with a healthy Betta that was being treated for fin damage with salt...they can usually tolerate going from salt to fresh, however, it is never a bad idea to do a day acclimation by making a 50% water change using fresh dechlorinated water for the replacement water while still in the QT or treatment container...then the next day make another 50% using the intended tanks water...net then add to the tank......provided that the Betta tolerate the 50% with the tank water.....